[release/9.0] Remove package baseline

[Copilot]

Backport of #64337 to release/9.0. Removes baseline mechanism.

Description

The package baseline system tracked dependency versions across servicing releases but the code path was never executed in practice. This removes:

• Baseline files: eng/Baseline.xml, eng/Baseline.Designer.props (1,115 lines)
• Generator tool: eng/tools/BaselineGenerator/ (3 files, 432 lines)
• Build logic: Baseline validation targets, reference resolution, and PropertyGroups from Directory.Build.targets, Packaging.targets, ResolveReferences.targets
• Documentation: References in PreparingPatchUpdates.md, ReferenceResolution.md, UpdatingMajorVersionAndTFM.md
• Scripts: Baseline generation step from CodeCheck.ps1
• Solution entries: BaselineGenerator project from AspNetCore.sln and tools.slnf
• Project suppressions: SuppressBaselineReference items from Microsoft.AspNetCore.Components.csproj

Differences from 10.0: Uses AspNetCore.sln (9.0) vs AspNetCore.slnx (10.0), version numbers reflect 9.0.13.

Note: Changes to auto-generated files (ProjectReferences.props, RequiresDelayedBuildProjects.props, SharedFramework.Local.props, ShippingAssemblies.props, TrimmableProjects.props) that were unrelated to the baseline removal have been reverted.

Customer Impact

None. Internal build system simplification only.

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

Removes dead code that was never executed. Build and test validation completed successfully.

Verification

• Manual (required)
• Automated

Built multiple projects successfully: Microsoft.AspNetCore.Components, Microsoft.AspNetCore.Http. Restore completed without errors.

Packaging changes reviewed?

• Yes
• No
• N/A

When servicing release/2.1

• Make necessary changes in eng/PatchConfig.props

Original prompt

Backport the changes from PR #64337 ([release/10.0] Get rid of package baseline) in dotnet/aspnetcore to the release/9.0 branch.

Context:

• Original PR: [release/10.0] Get rid of package baseline #64337
• Intent: Remove the package baseline in release/9.0 in the same manner as was done for release/10.0.

Requirements:

• Cherry-pick or reapply the commits from PR [release/10.0] Get rid of package baseline #64337 onto release/9.0, resolving any conflicts appropriately for the 9.0 codebase.
• Ensure any version-specific paths, package names, or baseline configurations that differ in 9.0 are handled correctly.
• Build and run tests to verify there are no regressions.
• Update any documentation or configs if the package baseline removal affects them.
• Prepare a PR targeting release/9.0 with a clear description including links to the original PR and a summary of changes.

PR description should include:

• "Backport of [release/10.0] Get rid of package baseline #64337 to release/9.0"
• Notes on any differences from the 10.0 change, if applicable.
• Validation steps performed.

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[wtgodbe]

Some feedback

[Copilot]

Pull request overview

This PR removes the package baseline mechanism from the ASP.NET Core 9.0 release branch, backporting changes from #64337 (release/10.0). The baseline system tracked dependency versions across servicing releases but was never executed in practice.

Changes:

• Removes baseline files (Baseline.xml, Baseline.Designer.props totaling 1,115 lines)
• Deletes the BaselineGenerator tool (3 files, 432 lines of code)
• Removes build logic for baseline validation and reference resolution from MSBuild targets
• Updates documentation to remove references to the baseline system
• Removes baseline generation from CodeCheck.ps1 script
• Removes project from solution files and cleans up project suppressions

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
eng/Baseline.xml	Deleted 113-line baseline package list (9.0.10 versions)
eng/Baseline.Designer.props	Deleted 1,002-line auto-generated baseline properties file
eng/tools/BaselineGenerator/README.md	Deleted tool documentation
eng/tools/BaselineGenerator/Program.cs	Deleted 398-line baseline generator implementation
eng/tools/BaselineGenerator/BaselineGenerator.csproj	Deleted project file
eng/targets/ResolveReferences.targets	Removed baseline reference resolution logic and validation
eng/targets/Packaging.targets	Removed baseline version validation target
Directory.Build.targets	Removed baseline import and version override logic
eng/Versions.props	Removed ValidateBaseline property
AspNetCore.sln	Removed BaselineGenerator project entries
eng/tools/tools.slnf	Removed BaselineGenerator from solution filter
src/Components/Components/src/Microsoft.AspNetCore.Components.csproj	Removed SuppressBaselineReference items
eng/scripts/CodeCheck.ps1	Removed baseline regeneration step
eng/Dependencies.props	Removed baseline-related comments
docs/UpdatingMajorVersionAndTFM.md	Removed baseline update instructions
docs/ReferenceResolution.md	Removed baseline documentation sections
docs/PreparingPatchUpdates.md	Removed baseline update instructions